Collimation

[bing434]

I'm wondering how often users of reflectors collimate their scopes. Will an uncollimated scope be that detrimental to viewing? In my backyard the LP is quite bad so I'm only able to view the brighter objects - moon, Saturn and Mars atm - how does poor collimation affect these objects?

The main reason I ask is because I can view Saturn and the moon and produce nice levels of detail. But Mars just appears as a bright reddish disc with no discernible features, even at low power. I understand that the Earth is accelerating more and more from Mars so it's far past its best. Out of interest, when will Mars be next in opposition? 18 months or so?

Can anyone recommend a decent, but cheap, laser collimator?

[brantuk]

I have a laser collimator for sale as I'm upgrading to a Hotech. It's a Skywatcher Premium - only used once or twice, boxed and in mint condition. PM me if you're interested.

Cheers

[Moonshane]

I collimate my dobsonian every time I use it. you don't mention the specification of your scope but basically, the lower the focal ratio (f5, f6, f8 etc) the more critical it is to viewing. you will still be able to see objects but there levels of sharpness and contrast will reduce if not collimated.

google 'barlowed laser collimation' and you'll find some ways to make it very easy.

[boboco]

Regarding the effect of lack of collimation at different degrees of collimation see here Thierry Legault - The collimation.

Regarding a collimation tool (assuming your refering to a newt/dob)..

Yes, a cheshire! With lots of thanks to albedo0.39 to for setting me on the right path. I struggled for a long time with an expensive (Kendrick) laser and never got good collimation, once I was shown how to properly collimate with a cheshire its much more efficient.

Problem with a laser is that any slop in the mounting (and there will be) means you can not be sure of the centre being hit and you have to be correct to within a millimeter with the laser to get good secondary alignment. (Some lasers like the hotech try to aleviate this - but there are other moving parts in the focuser not just the compression ring and you need to be sure that the laser itself is properly colluimated).

Cheshire is much better for this once you understand how to use it properly.

Alignment of the primary can be done either wilth a barlowed laser or the cheshire again.

I think albedo0.39 has a presentation on how - try to pm him, or get along to a club as its much easier if you have a guide the first time.

Cheers,

Karl.

[Moonshane]

Karl is quite right that slop in the focuser is a problem. BUT barlowing the laser gets around this and there's no effect due to slop as the barlow spreads the laser beam and you are collimating the primary to the reflection of your primary mark, not the laser dot.

you do still need to sort out the secondary with the laser first.

to be honest I generally have a quick check with a Cheshire (although it's usually spot on) after the collimation with the laser. the laser just makes the process quicker with my five foot long OTA! others also do a star test after whatever method they use but I have not mastered this yet.

I agree with Karl on trying to get someone to show you as it's much easier than it sounds no matter which method you use. once you have the idea of collimation and can do it, try putting it out of collimation and see what the difference is. actually, I should do this as it's not something I have tried! :0)

[bing434]

Yeah that's a good idea, thanks, all of you. I think I might ask some members of my local AstroSoc for some advice - probably best to get someone with experience to show me.

[Moonshane]

no worries. hooking up with others is also a great way to 'review' kit before you buy it for yourself. most people who have eyepiece X or filter Y will not mind you using it for short time at an event or what have you in your own scope. that way you can see it it suits you and does what you want it to do for you in the actual equipment you will be using it in. this is worth its weight in gold.

plus of course, it's always nicer to 'talk stars' with someone whilst watching. luckily my neighbour is also into astronomy and it's always far more enjoyable when we team up.

[TheThing]

Follow the advice given by Andy's Shot Glass video tutorial and you wont go far wrong. Most problems with focuser slop and lasers comes from trying to collimate with the scope horizontal rather than at the normal angle of viewing.

I've been visually collimating, but bought a laser collimator at SGL5 and it is much faster and more accurate.

The question of when to collimate is another one that causes consernation in people. I have a fairly fast Newt. It was collimated 2 years ago by Paul Money and has held very well (including a trip from Lincolnshire). It only needed a slight adjustment after going to and from SGL5.

If you're careful you can get away with/only need to collimate smaller Newts maybe once a year. Bigger Newts (10" plus) might need it more often - every couple of uses possibly.

Those with small, fast Newts how collimate more often are, IMHO, doing it unnecessarily and making work for themselves.

[ZOG]

I collimate before every oberving session. I bought a commercial barlowed laser and target for this so the whole operation only takes a couple of minutes but an ordinary barlow, in front of a laser, and a home made target will get the job done no problem.

[albedo0.39]

Owning a truss tube dob, you get very used to collimating (well, I do anyhow) and would advise a quick check prior to any serious observation.

Collimation affects the contrast and ability of the image to resolve so bright planets may not show bad collimation as much as the deep sky objects or close doubles.

Regarding the "cheap" laser, then beware... a better bet is a trusty cheshire. Master this, and you will not go far wrong.

Good luck

Steve

[nicnac]

i own a Hotech laser collimator which i use every time i set up and time after time it says "spot on"

bit then what would you expect, i use a TAL, i would have to drop the OTA out of the bedroom window to take it out of alignment

[vlebo]

This is handy if you use a laser collimator and have focuser slop.

Orion Precision Eyepiece Centering Adaptor

[acey]

I collimate my 12" f4.9 flextube every time I use it. When I used an 8" f6 I collimated only a few times a year and it worked well enough for me. With the 12" I use a laser (Antares) for the secondary and a cheshire for the primary and it takes a couple of minutes; with the 8" I used a punctured film cannister which took ages (and still probably wasn't right).

Poor collimation will have a more noticeable effect on planetary detail than on faint DSOs, but if you're enjoying the views then you've got nothing to worry about.

[bing434]

Ok maybe I shouldn't be that concerned. But the difference when I look at Saturn compared to Mars is astounding. Mars just looks like a pinkish coloured disc; no dark spots and no polar caps.

[LukeSkywatcher]

Ok maybe I shouldn't be that concerned. But the difference when I look at Saturn compared to Mars is astounding. Mars just looks like a pinkish coloured disc; no dark spots and no polar caps.

That sounds normal for visual observations. Mars is a REALLY tricky planet to observe and the "seeing" conditions of the sky have to be pretty good/stable to see any kind of detail.

Depending on the size of your scope, you may need to collimate more often for bigger scopes(10"+) and less for smaller scopes (5-10").

I have collimated my 5" scope once since i got it in early Dec 2009. It was pretty spot on then and it still is. I was concerned about it for a while but you could go insane worrying about collimation.